Circuit controlling method and apparatus



Feb. H, 1936. H ;l GRAVES, JR

CIRCUIT CONTROLLING METHOD AND APPARATUS 5 Sheets-'Sheet l Filed March 15,' 1933 @kwa QM V m m u @M ./f p W ,L .ed

Feb. 1l, 1936.

H. C. GRAVES, JR

CIRCUIT CONTROLLING METHOD AND APPARATUS Filed March 15, 19:53

zza

5 Sheets-Sheet 2 INVENTOR.

l ATTORNEY.

Feb. 1l, 1936. H. c. GRAVES, JR

CIRCUIT CONTROLLING' METHOD ND APPARATUS 5 Sheets-Sheet, 5

Filed March 13, 1933 INVENTOR.

MLN @gw l ATTORNEY.

NVENTOR.

5 Sheets-Sheet 4 :1 ATTORNEY.

Filed March 13, 1933 H C GRAVES, JR

CIRCUIT CONTROLLING METHOD AND APPARATUS f /////./////ff//// Feb. 11, 1936.

NVENTOR 5 Sheets-Sheet 5 H C GRAVES JR CIRCUIT CONTROL-.LING METHOD AND APPARATUS Flled March 15, 1953 Feb. 11, `1936. l

the chamber in 4lamented Feb. 11, 193e Herbert o. Greve., Je.. sus matera Township, .Chester County; Pa.,l assigner to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation oi New Jersey Appuesuen meen 1s, 193s, serial No. man

My invention relates to methods and apparatus for interrupting electrical circuits, and more pai'- ticularly to switches, circuit breakers and the like.

In accordance with one aspect ofmy invention.

5 the arc incident to opening of a switch or circuit breaker is transferred from the switch or breaker contacts to an extinguishing chamber along a path which facilitatesthe transfer to the chamber and substantially prevents flow of arc gases of reverse direction toward the contacts.

More specincally, the chamber is formed by stacked plates of insulating material having aligned openings forming thechamber, and which preferably, due to the shape of the openings, is provided with one or more convergences toward which the arcv is forced, as by a magnetic iieid. to ensure extinction of the arc whether largeorsrnall; transferof thearcisassistedby zo plates of metal interposed between and spacing the aforesaid plates of insulation, which metal plates also preclude now of conductive gases from the chamber toward the switch contacts.

In some forms of my invention. the stack of plates may include plates which in whole or in part are of magnetic material, to increase the speed of movement of the arc toward the extinguishing chamber and/ or to force it toward the aforesaid convergences o! the chamber walls.

My invention also resides in the features of construction, combination and arrangement hereinafter.. described and claimed. s

For an understanding of my invention, and for illustration of several modifications thereof. ref- 354 erence is to be had to the accompanyingdrawings, in which: A

Fig. 1 is a side elevational A.View withparts in section (line I-I of Fig. 2)

of a circuit breaker utilizing the invention.

Fig. 2 is a front elevational view. partly in section, of the structure shown in 1 (left half taken on line 2B-2B of Fig. l; right half taken on line IA-lA-of Fig. 1).

Fl'gs. 3-8 inclusive are detail views o! parts shown in Figs. l and 2.

Fig. Sais an explanatory gure.

Figs. 4a and 4b on/-reduced scale illustrate modiilcati'ons of the/plate structure shown in F18. 4. f

Fig. 9 diagrammatically illustrates the wiring of the circuit breaker of Figs. 1 and 2.

Fig. l0 illustrates another circuit breaker utilizing a modiedV type of extinguishing chamber.

Figs. 10a and 10b are detail views of moditlca- 28 (CL 20F-144) tions of the laminated arc-extinguishiilig` chamber Figs. ll to iii are detail views of the plates or elements forming the chamber ci' Pig. 10.

Figs. 12o and 12b on reduced scale illustrate 5 modifications of the plate structure shown F18. 12. i

Fig. 14 illustrates in front elevation the relative positions of the plates of Figs. 1l to 13 whe assembled. 10

Figs. l5 and 18 show composite elements for Fig. 17 is a side elevation 'of an assembly utilizing plates similar to Pig.' 15.

Fig. 18 is a detail view oi' the thermal tripping 13' element for the circuit breaker of Fig. 10.

Fig. 19 illustrates diagrammstically the wiring of thecircui't breaker of Fig. l0.

vlteferringtoll'ig.1,themovvablecontact I is heid in exceed emma position te bridge the si-.e- 2

tionary contacts! and Sbyanover-travelled toggieccmprising the link 4 connected at one end 'tothearmlofthehandlemember,andatthe s otherendtctbemovablearmIcarryingcontact l. Tnenandielmeybemtedwbreektneteg- 25 gletopermitaspringnotshowntoefiectopening of contact Lorthetngglemaybe brokeninresponse to circuit conditions otherthan normal. For example, thetrippin coil l upon occurrence o: overleed-11m the armature swmen strikes the 3 pin Iltomovethehandleupwardlytoopenthe 'nie ue :nement te epenmg'ef ne breaker 1s preferably drawn between the arcing tip Il carl" time of current iiow through the oven-current device during the interruption of overlcads, thus avoiding excessive stresses and heating.

Betweenthearcingplatesareaseriesofaperturedplatesox'laminationsIl,sucha.sshownin tinguishing chamber C. 'Ihe plates are held in po'sition by'bolts IB, I6, and I1 which are in/ sulated from the arcing plates I2 and I3. The upper central portions Il ofthe plates Il (Fig. 3) serve to reduce the cross-sectional area of the chamber by forming a ridge depending from the top of the chamber along itsflength; or otherwise expressed, the chamber converges at a and a', and more particularly it is connected by the converging passages I9 and I9 to the aligned openings 2li and 2I of the plates which form discharge passages as hereinafter explained. n

'I'he arrangement insures contact of the arc with a large area of cooling surface for chillingY the arc gases s uiciently to increase their dielectric strength above a critical value.

Moreover, the plates l I4 may be made of insulating material which upon contact with an arc liberates a gas or gases which chill the arc and extinguish it and prevent it from re-forming; for example, they may be of fibre or equivalent, which release hydrogen and/or carbon dioxide when engaged by an arc, or they may be of other material coated or impregnated with gas-produc'- ing chemicals, for example, boric acid. In general, the gases best suited have high specific heat and low density as hydrogen, water vapor, etc. Certain chemicals release powerfully effective gases when subjected to an arc but lose their dielectric strength at the time. With the stacked plate construction, it is possible to utilize such materials, as ammonium alum, and yet obtain 4proper dielectric strength for the stack by alter- Y posed the coils 22, 22a. which yare eiIective 'to move the arc upwardly into the chamber C and to force it into intimate contact with the converging wall structure of the chamber for chilling thearc gases. The coils 22, 22a are connected in parallel with each other and in series with the minals). As shown, the lower part of each coil induces a flux across the switch contacts and has a small radius of curvature, at this point to form j an intense eld for effecting rapid separation of the arc from the contacts. While it is preferred to use a pair of coils; a single coil is eiective in moving the arc upwardly into chamber C.

In an arc, a.` major portion of the current is conducted by a central core of gases at high temperature which is surrounded by gaseous cylinders whose temperatures are progressively lower outwardly from the core. The shell formed by the outer layers serves as an effective heat insulator for the core and permits a relatively low voltage to maintain an arc. core has a substantial thermal lag, the gases revmaining at high temperature throughout the cycles of alteration of the current. In my device, by forcing the arc into the convergences a, a of the will structure, the outer gas layers are dis- P torted, generally as shown in Fig. 3a, increasing 4.the temperature gradient between the arc core and leading boundary of the arc and so inl creasing the rate of transfer of heat yfrom the y composition of some gases, for example, of car- `bon-dioxide to carbon monoxide and oxygen.

So shielded, the arc.

i I'his device is eil'ective in extinguishing large `or small arcs because irrespective of the arc size it is forced into intimate contact with the quench-q lustratedin Fig. 4, while the upper parts of the plates Il are spaced by the washers 23 on the bolt I1. I'he metal plates 34 terminate between the upper and lower bolts so that recesses between plates" Il exist on either side of the main chamber C and above the metal plates. These openings extend to the top of the structure forming vents for the discharge of gas.

The effectiveness of the arrangement is increased by this spacing of the plates Il, for in effect the `cross-sectional area of the chamber CA along its length varies abruptly from the width .'r, Fig. 3, to the width of the spacing between the walls 24 of the housings 25 for the arc transfer coils 22, 22a. As a result of the axial ow, the

arc gases are violently agitated or mixed with the chilling gases which more readily penetrate into the arc core and'chill it. y

Turbulence splits the arc stream into threads which become more numerousand tenuous. as the Y turbulence increases in violence. -The thermal lag of the threads is insubstantial so that their temperature iiuctuates widely, closely following the alternations in current. This makes it easier to chill the arc gases, and thus to restore the dielectric strength of the path. The'condition which prevents reforming of the arc after the current pases to zero is that the dielectric strength of the gases or rather the breakdown voltage must increase more rapidly .than the applied voltage. In operation, the action of the device is so rapid that the art is usually extinguished `at the rst current zero after commencement of the arc or within a half cycle.

lThe openings between the 'top edges of the spacedy plates I4 may be closed, as by a' cover plate overlying them. A space between the top of the plates and the bottom of the cover may be advantageous. Again they may be left open, in which case, thevlength of the path to the top edge of the plate should be sufficiently long to prevent the gases issuing from the opening from being in such state that there is any likelihood of re-establishment of the arc outside of the device.

The formation of the arc, its transfer, and the generation of gases by the arc follow in such rapid sequence as to be practically instantaneous. The generation of gases is 'so rapid that the ex- `tinguishment of the arc is accompanied by an explosion. To reduce the noise of the report, it is desirable to break the sound waves by the mufiie plates 2'I.v I'he openings 28 in the plates 21 are sufficiently large to offer insubstantial resistance to the flow of the gases from chamber C to atmosphere. As shown in Fig. i, the munie plates 21 may be supported by the bolt I1 which extends through the central openings 29 thereof. The plates 21 when of metal are insulated from l s,oso,ssa

the bolt by tube 3l and are suitably spaced from each other by washers Il of suitable insulating material.

To increase the volume of gases liberated, either or both of the arcing plates may be composed. at least in part. of a conductor. as carbon, which liberates chilling' gases when heated by. the arc. For example, the back plate I2, may be provided with a member t! of carbon having an arcing tip I3 extending into the rear of chamber C.

I'he transfer of the arc from its source to the extinguishing chamber C is facilitated by making the plates 3l of conducting material, preferably brass, copper or a conducting alloy which gives of! chilling gas at relatively low temperatures which, as shown in Fig. l, are spaced from each other, as by the lower portions of the laminations Il.l The arc travels upward toward the chamber in the form of a seriesof short arcs between the plates 34. Alternate plates are disposed so that their upper inclined edges l! pointin one direction while the intermediateplates are arranged so that their upper inclined edg Il ex-` tend in the other direction, Fig. 2.

As each are section travels' `upwardly into chamber C, between adjacent plates 34, itis lengthened due tothe divergence of the upper' edges of the plates; The arc as a whole zig-zaga between the `upper diagonal edge o f the plates, increasing in length as the upper ends of plates 34 are approached.

In lieu of plates of the shape shown in Fig. 4, there may be used plates 34a, Fig. 4a whose top edge is horizontal instead of sloping: or as shown by Fig. 4b. may be each replaced' by two plates 34h, c which when in assembled position have their adjacent edges approaching each other in the direction of movement of the arc, leaving a narrowslotsatthetopedgesoftheplatewhich may be horizontal, downwardly inclined from the slot, or any other desired shape.

The upwardly acting force of coils 22, 22a., the stretched condition of the arc, the generation of gasasthearc contactswiththeedgesofthe laminations I4, the gas velocity along the axis of the chamberall combine to free the arc from the plates and throw it against the central ridge at the top of the chamber for liberation of chillin'g gas as previously described.

'I'he bolt I1 is preferably of magnetic material to increase the intensity of the iiux at the ridge so that the arc is pressed hard against its sloping surface and forced into the converging slots il, i9'. The intense field ensures intimate contact of the arc with the insulating material for enhanced chilling and for generation of large volumes ofchillinggas. Theareandgenerated gases now from the chamber at hig velocity due to high pressures developed.

Thespacingbetweenplatesuissonarrow with respect to the openings between.. the munie plates 21 that a back pressure is built 'up which greatly restricts the downward now of the gases. The chilling effect of these plates substantially prevents the now lof conductive gas to the `brealrer contacts. The maior flow *of the gasesis along the main chamber C and the auxiliarypassages 2li, 2l. The now here is unrestricted and ex'- tremely high velocities are attained.

A preferred wiring arrangement for the breaker is shown in Fig. 9. The conductor D is connected as indicated so that the arc current-does not traverse the tripping device l after transfer of the'arc'to plates I3 and I2.

Referring to mg. 1o fo'mustraaon or another circuit breaker utilizing the invention, when the current through the tripping coil 16 is sui'ncient- 1y high to actuate the larmature 11 to tripping position, the movement of the latter breaks the toggle 18, 18a to allow the spring 19 to move the movable contact member 80 away from the sta- A tionary terminal l-a and toward open-circuit position irrespective of whether handle 8|A in the position shown is free or held manually. The

outer terminal of the arc is transferred from the movable contact tip 82 to the-iront arcing plate B3, as in the modification of Fig. 1.

In this modincation, thef'arc current ows through the bolts 8l through conductor 85 to the lower terminal of the circuit breaker to magnetize the iron laminations 8B*z (Fig. 13) The direction of current through the bolts is reversed with respect to the iiow of current in the arc and the flux produced between the legs l1, 81 of the laminations moves the arc upwardly toward and intoy the extinguishing chamber C where it is forced against the convergence a of the insulation laminations 88 (Fig. 11) for chilling of the arc, generally as previously described. The gases discharge axially of the chamber through the openrestrict the passage of Iconductive gases downwardly-toward the switch' contacts. Also as in Fig. l, adjacent copper laminations may have upper inclined surfaces directed in opposite directions to force I'the arc to zig-.zag between them and increase in length as it is forced upwardly by the Vaction or the iron laminations, or more specifically; by the interaction between the eld of the arc and the field of the plates 8B.

In lieu of the plates o f Fig. 12 with inclined upper edges, there may be used plates IS-a, Fig. 12a, having top edges which are substantially horizontal, or preferably, each plate may be replaced by two plates lsb, 89e, Fig. 12b, which when assembled in the stack, have their adjacent edges converging upwardly and separated at thetopbyagaps. v

By. way-of example, in the above construction the copper, iron, and nbre laminations may each be about one-sixteenth inch in thickness affording for ea'ch group in the assembly about 25% iron, nbre, and 25% copper with a vent v.

at the top, of 25% as-most clearly shown in Fig. 10a.

'I'he .velocity of the arc, the rate of discharge of the gases, and the life of the f lbremay be increased by utilizing the modification shown in Figs. 15 and `lil. The lamination 9|) (Fig. l5.) is composite in that-it is formed of two iron legs Il, li joined by a member 02 of copper, or brass. This lamination replaces the all copper or brass elements 09 (Fig. 12K) and may be three-thirtyseconds of an inch thick. With fibre laminations 88a, about one-eighth inch in thickness, an iron laminationl 86 of about one-sixteenth inch thickness and the aforesaid composite lamination, the ratio for cach group of the assembly is about 441/295 nbre, 551/&% iron, and 33E/3% copper, with a vent of 336%. The increase in iron-is berie- ,iicial particularly for the smaller arcs.

The assembly as shown in Fig. 10b may also be built of composite laminations 93, Fig. 16,

alternating with fibre laminations 88a in which case, all of the discharge will take'place. at the end of chamber C. The nbre laminations 88aand the composite laminations 93 may be of the order of one-eighth inch in thickness. This compite lamination comprises an iron horse shoe with a non-magnetic plate 94 and an insulating lining 95 for the chamber C.

The tripping arrangement for the breaker is generally similar to that described and claimed in my application Serial No. 632,527 iiled September l0, 1932. Briefly, the lower end of armature 11 normally engages a magnetic stop 36 which is an extension of the lower pole piece 38 of the tripping coil 16. Under normal conditions, the stop 36 restrains the armature from clockwise movement. Upon occurrence of very heavy overloads, the attraction of pole 38 predominates, due to saturation of extension which is of reduced cross section, andinstantaneous opening of the breaker is effected. For sustained lighter overloads, tripping is effected by thec U-shaped bimetallic strip 3l which bends downwardly so that the cam member moves armature 11 from stop 36 to a position at which the attraction of pole 3l predominates whereupon armature 11 is magnetically actuated to tripping position. u

As shown most clearly in Fig. 19, conductor connects the front arcing plate to theline side of the thermal strip 39 so that the arc current does not traverse it to cause burning particularly at the bend of the U.

While several preferred arrangements have been illustrated, it is to be understood that my invention is not limited thereto but is co-extensive in scope with the appended claims.

What I claim is:

l. An arc extinguishing device comprising a substantially conilned arc extinguishing chamber, and means including a plurality of spaced conductive plates extending adjacent the arc source for transferring the arc to said plates and dividing it into a plurality of arcs extending therebetween, said conductive plates Vterminating in said chamber to facilitate the transfer of the arc thereto and terminal plates within said chamber spaced-for formation of at least one arc therebetween of substantially greater length than any one of said plurality of arcs.

2`. An arc extinguishing device comprising a substantially confined arc extinguishing cham- ,ductive plates terminating in said chamber and y extending in spaced relation' adjacent the arc source, and magnetic means for electing movement o'f the arc along said plates into said .chamber and toward said converging vented wall structure thereof.

4. An arc extinguishing device comprising r alternate laminations of conductive material and insulating material, the laminations of insulating material forming a substantially coniined explosion chamber and the laminations of conductive material terminating in said explosion chamber to facilitate the transfer of the arc thereto from the arc source and forming restricted pas- `spaced relation adjacent the path of the arc between said switch electrodes for facilitating transfer of the arc to said chamber and for restricting passage qf incandescent gases within said chamber toward said electrodes.

6. An arc extinguishing device for a switch comprising a substantially confined explosion Bchamber, electro-magnetic means for effecting transfer of the arc from the switch electrodes to said chamber, and means for facilitating transfer of the arc comprising a plurality of conductive plates terminating in said chamber and extending in spaced relation adjacent the path of the arc between said electrodes.

7. An arc extinguishing device comprising a coil whose axis issubstantially normal to the arc, an. explosion chamber whose axis is substantially parallel to the arc and which is substantially removed from the source of the arc, and a plurality of spaced conductive .plates tenninating in said chamber and extending substantially parallel to the axis of said coil adjacent to the arc source.

- 8. An arc extinguishing device comprising a substantially conned explosion chamber having internal wall structure of insulating material, plates in said chamber for forming the terminals of a single long arc, and a plurality of spaced conductive plates entering' said chamber for transfer of the arc from its source into said chamber.

9. An arc extinguishing device for a switch having separable electrodes comprising a substantially confined explosion chamber having internal wall structure, a substantial vportion of which is of insulating material, means for effecting transfer of the arc from said electrodes to said chamber, arcing terminals within said chamber for receiving said arc, at least a portion of one arcing terminal comprising carbon to liberate arcchilling gases in said explosion chamber when heated by the arc; and a vent for said chamber disposed for flow of gases axially of the lplates into said explosion chamber.

11. An arc extinguishing device comprising arcing plates, a stack of laminations` between said plates having aligned openings forming a substantially conned .arc quenching chamber, *and mume plates in the path of gases flowing from said chamber.

12. An arc extinguishing device comprising a plurality of composite laminations, each lamination having a part formed of insulating material and at least another part formed of conductive material, said laminations being provided with openings disposed tp form va substantially coniined arc extinguishing chamber, terminals within the chamber for a single long arc, and spacers formed of insulating material interposed be-' tween adjacent laminations, said conductive portions of said laminations entering said chamber for transfer of the arc therebetween from its source to said terminals in said chamber.

13.c An arc extinguishing device comprising a substantially confined arc-extinguishing cham--J ber and a relatively narrow passage extending thereto, said chamber having internal wall structure of insulating material, and said passage having wall structure including magnetizable material for producing a magnetic field for moving an arc through said passage into said chamber.

, 14. An arc extinguishing' device for a switch comprising a substantially confined explosion chamber, electro-magnetic means for effecting transfer of the arc from the switch electrodes to said chamber comprising a plurality of plates, a non-magnetic portion of each plate being conductive and terminating in said chamber, elements of insulating material associated with said plates and forming an insulating lining for said chamber.

15. A circuit-interrupting device comprising switch contacts, electro-responsive means for effecting separation of said contacts connected in series therewith, and arcing plates to which the arc between said contacts is transferred, connected in shunt to said contacts and said electro-responsive means.

16. A circuit-interrupting device comprising a fixed contact,'an arcing plate connected'thereto, a movable contact, electro-responsive means for effecting separation of said contacts having a terminal connected to said movable contact, a second arcing plate to which is transferred the aro terminalinitially formed on the movable con tact. and a connection from said second plate to another terminal of said electro-responsive means to exclude said movable contact and electro-responsive means from circuit upon said transfer of the 17. A circuit-interrupting device comprising a fixed and movable contact between which an arc is drawn, a thermal-device traversed by the current traversing said contacts and adapted to effect their separation for excess magnitudes of said current, arcing plates, means to effect transfer of an arc from said contacts to said arcing plates, and connections excluding said thermalv device from the circuit of the arc upon transfer' of the arc to said arcing plates.

18.A circuit interrupting device comprising a substantially conned arc extinguishing chamber, a plurality of conductive laminations, the entrance to said chamber lying between said laminations and extending into said chamber for transfer from its source into said chamber of the arc as a plurality of short arcs, terminal plates within said chamber spaced one from the other and between which a plurality of the short arcs unite, means subjected to the heat of the said arcs for generating gas within said chamber, and a vent for said chamber of greater cross-sectional area than said entrance to insure exit of the gases in a direction away from the arc source.

19. A circuit-interrupting device comprising contacts between which an arc is drawn, arc

terminal plates to which the arc is transferred, a

stack of plates of insulating material between said terminal plates having substantially aligned openings forming a substantially conned extinguishing chamber, means for facilitating transfer of the arc to said chamber and for preventing flow of conductive gases from said chamber toward said contacts comprising metal plates in- 5 terposed between plates of said stack and terminating in said chamber, and means for accelerating the transfer of the arc and for pressing it against the wall structure of said chamber comprising plates of magnetizable material interposed between plates of said stack.

20. 'Ihe method of extinguishing an arc which consists in dividing the arc into a plurality of short arcs, in a substantially confined chamber moving said short arcs at angles one to the other and simultaneously lengthening each arc, in said chamber recombining a pluralityof said arcs to li'orm at least one relatively long arc, and by the arc heat generating arc-influencing gases.

' 21. A circuit-controlling device comprising separable contacts, a stack of laminations having aligned openings forming a substantially confined explosion chamber substantially removed from said contacts, arc terminal contacts at opposite ends of said chamber. a plurality of closely spaced conductive plates included in said stack and terminating in said chamber to facilitate transfer of the arc to said chamber for rei'ormation as a single long arc therein between said terminal contacts and to restrict ow of conductive gases from said chamber toward said separable contacts, -means producing a ux for moving said arc against gas-releasing insulation in said chamber, and means for allowing escape of gases from said chamber in a direction away from said contacts.

22. An' arc-extinguishing device comprising slotted plates of conductive material having inclined upper edges, and means forholding said plates in a stack with their slots in alignment- 40 and with the inclined upper edges inclined in opposite directions.

23. An arc extinguishing device for a switch having contacts relatively movable to an open circuit `position with formation of anu arc therebetween, a substantially conned arc extinguishing chamber spaced from said contacts, means sub-dividing said arc for transferring the subdivisions thereof into said chamber, the heat of said arc generating gas pressure within said chamber, insulating material lining at least a portion'oi' said chamber and of a character for liberation of gases to augment said gas pressure, and means producing a high velocity gas flow within said chamber comprising a discharge vent separate from the entrance to said chamber and alternately through which said gases are expelled; C

24. An arc-extinguishing device for a switch comprising a substantially conned elongated arc-extinguishing chamber provided`with a restrlcted longitudinal openings adjacent to and closely spaced along the path of movement of the switch contacts, and means for transferring an arc from the switch contacts through said restricted openings to said chamber, and means in arcs. with adjacent arcs at a substantial angle to each other and to the path of movement of said contact structure, and means for converting the pressure developed by said arc into a blast substantially normal to said short arcs to extinguish them. l

26. An arc-extinguishing device for a circuit interrupter comprising a plurality oi' plates of conductive material adjacent to and closely spaced along the path of movement oi the movable contact structure oi' the interrupter and normal thereto, said plates having their edges remote from said contact path alternately inclined .in opposite directions, means for transferring an arc from the contact structure of the interrupter to said plates and across said plates to said inclined edges to cause it to assume a. zigzag form, and means for converting the pressure developed by said arc into a blast substantially normal to said plates.`

2'7. An arc extinguishing device for a switch comprising an explosion chamber having internal wall structure of insulating material which liberates chilling gas when engaged by an arc, a plurality of closely spaced conductive plates terminating in said chamber and extendingA adjacent the path of movement oi movable contact aoaassa structure or the switch to receive the arc and transfer it away from said contact structure as a series of short arcs into said explosion chamber and contact plates spaced longitudinally of said chamber for the formation therebetween o! a relatively long arc.

28; An arc extinguishing device comprising a plurality oi substantially U-shaped laminations oi magnetic material, non-magnetic conductive members bridging the legs of said laminations, a plurality o! Ufshaped laminations oi insulating material alternating with said rst-named laminations to form in conjunction therewith an elongated arc extinguishing chamber, said chamber having openings thereinto extending between said conductive bridging members, elements'i'ormed o! -insulating material lining said iirst laminations opposite said bridging members. said magnetic laminations cooperating to move into said chamber a plurality ot short arcs extending between said conductive members, means in said chamber for -formation of a longarc therein,and a vent at one end of said chamber for converting the pressure developed by said arc into a blast substantially normal to said laminations.

l HERBERT c. GRAVES, Jn. 

